The present invention relates to improvements in apparatus for controlling the exposure of solid state image sensor arrays of the type proposed for use in electronic cameras, facsimile equipment, and the like.
Linear and areal arrays of solid state photosensors (e.g. charge coupled devices (CCD's) and charge injection devices (CID's)) have now been produced with packing densities sufficient to warrent their use as high resolution optoelectric image converters in electronic cameras and facsimile equipment for converting optical images to electronic form. To prevent overexposure of these arrays and thereby prevent the so-called "blooming" of photosites and the distortion resulting therefrom, there is a need to maintain the exposure level of the array within certain tolerances.
In U.S. Pat. No. 4,131,919, issued to G. A. Lloyd et al, there is disclosed an electronic still camera in which an image formed on a charge coupled device array is converted to electronic form and recorded on a magnetic storage medium. The exposure of the CCD array is controlled by a conventional photoelectric circuit which controls the opening in a diaphragm positioned in front of the array. While this technique of exposure control is technically sound, the use of an auxiliary photoelectric exposure control circuit is undesirable, at least from the standpoint that it can add significantly to the manufacturing cost of the camera.
It has been proposed heretofore to use a solid state image sensor array as the light-sensitive element in exposure control systems of the type used in photographic cameras. For example, U.S. Pat. No. 4,047,187, issued to Mashimo et al, discloses the use of a CCD array to control both the exposure of a photographic film and the focus of the camera's lens. In the camera of Mashimo et al, the CCD array is relatively small in terms of the number of photosites, and its output is dedicated solely to the exposure control and autofocus functions using the output of the array to produce a television display of the image focused thereon.
U.S. Pat. No. 4,005,443, issued to Albrecht, discloses a photographic camera which, like the above-mentioned camera of Mashimo et al, employs a small solid state imaging array to produce signals for automatically focusing the camera lens. Additionally, the scanned output of the array is integrated to provide an exposure control signal which, by means of an adjustable aperture, prevents overexposure of the array itself. Here again, however, the array is dedicated to functions other than that of recording or displaying the image of information focused thereon.